The present invention relates to certain etherified or esterified starch derivatives which form relatively low to moderate viscosity solutions when dissolved in water at a starch solids level of about 10 weight percent on a total solution weight basis and which form clear, transparent films upon drying from an aqueous solution thereof and to processes for the preparation of such starch derivatives.
As a general proposition, etherified and esterified starch derivatives such as, for example, methylated starch, ethylated starch, hydroxyethyl starch, hydroxypropyl starch, carboxymethyl starch, starch formate, starch acetate, starch propionate, starch butyrate, etc. are known materials. However, such materials as heretofore prepared have been of a type which exhibited relatively high viscosity in the form of aqueous solutions containing 10 weight percent of said starch derivative on a total solution weight basis and/or which did not form clear transparent films when dried from an aqueous solution thereof. As a result, these previous etherified or esterified starch derivatives have not been suitable for use as a replacement for low-to-medium viscosity natural gums (e.g., gum arabic, etc.) in various end-uses requiring a combination of cold water solubility, relatively low, stable viscosities in relatively high solids aqueous solutions and the ability to form clear, transparent films when dried from aqueous solution.
Also known in the prior art is the concept of depolymerizing or "thinning" starch or the various starch derivatives via the treatment thereof with enzymes such as amylases or with various acidic materials and the fact such treatment generally has the effect, depending upon the extent or severity of such treatment, of reducing the viscosity exhibited by aqueous solutions of the so-treated starch product. As heretofore prepared, however, acid or enzyme thinned starch products have been of a type which tended to retrograde upon standing in aqueous solution and/or which did not form non-hazy, transparent films when dried from an aqueous solution thereof. As a result, the previously available acid or enzyme thinned starch products have also not been suitable for use as a replacement for low-to-medium viscosity natural gums in the aforementioned end-use applications.
In view of the foregoing, it would be highly desirable to provide a means of obtaining a cold water soluble starch-based product having a combination of relative low to moderate, stable viscosity characteristics in relatively high solids (e.g., 10%, 25%, 40%, etc.) aqueous solutions thereof and the ability to form clear, transparent films upon drying from aqueous solution.